Tuck Everlasting(2002) [Winnifred 'Winnie' Foster]: Dies (off-screen) of natural causes, some time after her final scene; we learn of her death afterwards when the immortal Jonathan Jackson returns to her hometown many years later and discovers her headstone. (Thanks to Jake)

Sin City(2005) [Becky]: Shot to death (off-screen) by Josh Hartnett in an elevator; the scene cuts to black before anything happens, but Josh's MO as a hitman was established in an earlier scene when he kills Marley Shelton. (Thanks to Gary, Robert, Alex and Ric)